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std: sysatomics: fix use of atomicCompareExchangeN for MSVC (#25325)

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`InterlockedCompareExchange64 `(winnt.h) is used instead of gcc atomics
when compiling with MSVC on Windows, but the function signatures are
`InterlockedCompareExchange64(ptr int64, int64, int64)` and
`InterlockedCompareExchange32(ptr int32, int32, int32)` as opposed to
`(ptr T, ptr T, T)` for `__atomic_compare_exchange_n`.

Passing a pointer to the expected value (parameter two) instead of the
value itself causes the comparison to unconditionally fail, with stalls
in threaded code using atomic comparisons.

Fix the function signature for MSVC.

Signed-off-by: Ryan Walklin <ryan@testtoast.com>
This commit is contained in:
Ryan
2025-12-02 22:07:07 +13:00
committed by GitHub
parent 91febf1f4c
commit 2d0b62aa51
1 changed files with 4 additions and 4 deletions
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8
lib/std/sysatomics.nim
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@@ -230,11 +230,11 @@ elif someVcc:
proc atomicCompareExchangeN*[T: ptr](p, expected: ptr T, desired: T,
weak: bool, success_memmodel: AtomMemModel, failure_memmodel: AtomMemModel): bool =
when sizeof(T) == 8:
interlockedCompareExchange64(p, cast[int64](desired), cast[int64](expected)) ==
cast[int64](expected)
interlockedCompareExchange64(p, cast[int64](desired), cast[int64](expected[])) ==
cast[int64](expected[])
elif sizeof(T) == 4:
interlockedCompareExchange32(p, cast[int32](desired), cast[int32](expected)) ==
cast[int32](expected)
interlockedCompareExchange32(p, cast[int32](desired), cast[int32](expected[])) ==
cast[int32](expected[])
proc atomicExchangeN*[T: ptr](p: ptr T, val: T, mem: AtomMemModel): T =
when sizeof(T) == 8: